Constant current/constant voltage drive for an electrochromic display cell

Abstract

For an electro-optical display cell which manifests the electrochromic phenomenon to place the cell into the colored state or bleached state in response to current supplied, a constant current driving technique is carried through in the color (write) mode and a constant voltage is carried through in the bleach (erase) mode.

What is claimed is: 
     
       1. A display system comprising: an electrochromic display having a predetermined number of display segments having at least on and off display states, each of said segments being associated with individual display electrodes and all associated with a counter electrode;   writing means for applying constant current to said counter electrode to place said display in an on display mode;   erasing means for applying a constant voltage to said counter electrode to place said display in an off display mode; and   selection means for connecting the display electrodes associated with display segments desired to be changed to ground, said selection means further energizing said writing means or said erasing means in correspondence with the display mode desired;   said writing means varying the magnitude of current applied to said counter electrode in correspondence with the numbers of display segments to be placed in an on display state.   
     
     
       2. A display system comprising: an electrochromic display having a plurality of display segments, each of said segments being associated with individual display electrodes and all associated with a counter electrode;   writing means for applying one of a plurality of constant current levels to said display to place said display in an on display mode;   erasing means for applying a constant voltage to said display to place said display in an off display mode;   means for selecting those display segments desired to be changed and for connecting respective ones of said display segments to a node; and   means responding to said connections of each said segment by said writing means for applying one of said plurality of constant current levels to said display counter electrode to supply each segment with a constant current of a predetermined desired magnitude.